The items of equipment installed on board an aircraft and notably the flight management assembly must achieve the target level of safety, if the aircraft must implement required navigation performance with authorization required operations of the RNP AR type.
The objective is to have the capability of flying the RNP AR procedures with RNP values down to 0.1 NM, and to do so without restriction (in a normal situation and in the case of a failure) during departure, approach and go-around.
In order for an aircraft to have authorization to implement such RNP AR procedures, it is notably necessary to be able to eliminate an erroneous source of computing guidance instructions (or commands) from the guidance loop in order to counter its possible effects on the trajectory of the aircraft.
In order to be able to implement an operation of the RNP 0.1 type, the flight management assembly must make it possible to comply with a severity of the “hazardous” (dangerous) type in the case of loss of or error in the guidance commands. Moreover, it is necessary that, in the case of detection of an incorrect calculation, the aircraft can continue to be guided in automatic mode in order to be kept in the RNP corridor.
With a flight management assembly having two flight management systems, in the case of disagreement between then two flight management systems, the assembly is not capable of identifying which one is defective and the aircraft can therefore no longer be guided in automatic mode. Such an aircraft is not therefore authorized to implement such RNP AR operations.